The incumbency effect in the 2018 midterms

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With November’s general elections four months away, both parties are gearing up for an election that might propel Democrats to a majority – or might not. The House has attracted the most attention: Democrats need to pick up only 23 Republican-held seats in the 435-seat House to seize control of the chamber majority (they’d need only two Senate seats, but that’s an even rockier road to victory).

Fortunately for Democrats, they’ve been bolstered by a tailwind: Republicans are retiring from the House in droves, leaving “open” seats – races that lack an incumbent who seeks re-election – in their wake. Only 19 Democrats, compared to a 38 Republicans, will not seek reelection or are running for another office. GOP representatives have not opted out of re-election in these numbers since 1930.

These open seats have been central to Democrats’ efforts to retake the House, and for good reason: open seats are more likely to switch hands, whereas incumbents almost always win re-election.

This is no exaggeration. Since World War II, incumbents in the House have been reelected 93% of the time, and 80% of the time in the Senate. Even in wave elections, when the (usually minority) party overwhelmingly defeats another (usually majority) party, the effect is glaring. Consider the last four House wave elections: in districts that leaned away from the president’s party, 59% of incumbents from the president’s party still won – but when those seats were open, the president’s party clung on to only 6% of them.

Political scientists have studied the “incumbency effect” for decades and generated a number of possibly influencers, from pork-barrel spending and media coverage, to incumbent visibility and access to campaign finance. But these factors fall roughly into three categories:

  1. The selection effect: incumbents are simply better candidates (they won election for a reason, didn’t they?).
  2. The responsiveness effect: incumbents can showcase records of their actions in office – a political CV that newcomers lack.
  3. The institutional effect: incumbents take advantage of institutional structures to keep their seats safe from challengers.

The first and second effects assume that candidates are re-elected for being good politicians, like prize fighters that have earned a place in the ring. The third effect supposes that incumbents rely on systemic factors: They get “free” (franked) mail, attract more campaign money, have large and well-structured teams, etc. This would be fine if they stemmed from the first or second factor – i.e., Congressman Jane Doe serves her constituents so well that they donate to her campaign. In other words, if institutional insulation stemmed from voter awareness and approval, then it would be a sign of a healthy democratic process.

But that’s not always the case. Voter awareness alone is hard to achieve in the United States: a recent Gallup poll found that only one in three people could even name their congressman. Voter turnout doesn’t fare much better. Out of the 32 developed countries in the Organization for Economic Co-operation and Development (OECD), the U.S. ranked 26th in voter turnout, with just under 56% of the voting-age population casting ballots in the 2016 presidential election. Even this number looks lofty compared to midterm election turnout, which fell to 36% in the 2014 midterms.

Moreover, those who do vote tend to favor incumbents. In an odd twist of voter psychology, the one-in-three voters who can name their congressmen are far more positive about the member: it’s easier to disapprove of an entity like Congress than an individual – our local representative John Doe can’t be so bad, right? These one-in-three voters are also much more likely to vote, so those who turn out on election day tend to back their incumbent.

What does this mean for the 2018 midterms? As with all political predictions, it’s hard to say. But compared with midterms of the past two decades, voter engagement has sky-rocketed: 51% of registered voters say they are more enthusiastic about voting than usual, the highest percentage seen in at least 20 years. Democrats have a slight edge in this enthusiasm, and thus far, it has shown in the primaries: 5 million more Democrats have voted in the midterm primaries than in 2014, compared to only 2 million more Republicans – a 58% and 19% increase, respectively. If the usual one-in-three voter turnout spikes to, say, two-in-three voters, incumbents may be in for a tougher run.

That said, primary turnout doesn’t equal general election turnout. The election is months away, and political tides can turn rapidly. But with many more Republican-held seats than Democratic-held seats considered vulnerable (31 to 3), and Republican retirements at such high levels, it’s no wonder conservatives are worried: even incumbency may not be enough to save the GOP majority.

For an in-depth look at the facts and figures influencing the 2018 midterm elections, download our webinar: Wave or Ripple? A Look Ahead at the 2018 Midterms.

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